Process for burning fuel

ABSTRACT

A process for burning fuel which is formed of free hydrocarbons and/or fine-grained to dusty solid fuels, with a view to obtaining thorough mixing of the oxygen with the fuel in a manner as free of turbulences as possible, is characterized in that, into a main jet of oxygen or an oxygen-containing gas which is approximately cylindrical or slightly conically widening in the jet direction, several fuel jets oriented in a skew manner relative to the central longitudinal axis of the main jet are blown, which fuel jets are formed to surround the main jet peripherally, penetrate into the main jet and are sucked into the main jet.

BACKGROUND OF THE INVENTION

The invention relates to a process for burning fuel comprised of freehydrocarbons and/or fine-grained to dusty solid fuels, in particular ina metallurgical vessel. Furthermore, the invention relates to a burnerfor carrying out the process and a metallurgical vessel including aburner according to the invention.

Various types of construction are known of burners for burning gaseous,liquid or fine-particle solid fuels, in which oxygen or anoxygen-containing gas is supplied to the burner mouth separate from thefuels. Thus, for instance, from WO 91/06804 an oil burner is known, inwhich liquid fossile fuels emerge through a central tube and oxygenemerges through discharge openings provided radially about the centraltube and parallel thereto, wherein a partial amount of the oxygen isallowed to emerge from the burner at a low speed and the remainingoxygen is allowed to emerge from the burner at a high speed. This is toavoid nitrogen oxides.

From EP-A-0 347 002 a burner is known, in which oxygen, by means ofseveral oxygen jets which are directed against the axis of the burner atan angle of between 20° and 60°, is supplied towards solid fuel blown incentrally in the axial direction of the burner. This causes turbulencesand the intimate mixing of the oxygen with the fine-particle solid fuel.This involves the disadvantage that, due to the substantial highercombustion speed of combustible gases externally surrounding the burneror burner jet as compared to the combustion speed of the fine-particleto dusty fuel, poor burning out of the fine-particle to dusty fuelsupplied takes place. That known burner, furthermore, has thedisadvantage of causing whirling with the oxygen immediately uponemergence of the fine-particle fuels from the central inner tube suchthat a focal spot is formed located closely at the burner mouth. Thiscauses a high thermal load on the burner mouth and hence extensive wear.

A burner with which such an extensive wear is avoided is known fromEP-B-0 481 955. In the burner known from that document, the supply offuel is effected centrally and oxygen feeding occurs by means of oxygenjets peripherally surrounding the central fuel jet and inclined relativeto the central fuel jet, the point of intersection of the oxygen jetswith the fuel jet being located at a distance from the burner mouth.

A multi-media nozzle which may be employed also as a burner is knownfrom DE-C-42 38 020. That known multi-media nozzle serves to introducegaseous, liquid or pneumatically conveyable solid fuels as well asoxygen, the supply of the substances being effected through a centraltube and through one or several annular gaps surrounding the centraltube and defined by tubes arranged concentrically with the central tube.However, this involves problems with regard to the thorough mixing withthe oxygen of the fuels supplied to the multi-media nozzle.

From DE-A-36 12 682, JP-A-61-062704 and EP-A-0 368 829 it is known perse for axes of fuel jets from burners to be directed such that they areoriented in a skew manner relative to the axes of other jets emergingfrom the burner, for example in a skew manner relative to a central mainjet of the burner. Yet, in this, the arrangement is always chosen suchthat the fuel jets which are oriented in a skew manner relative to themain jet move away from the main jet from their site of origin onwards.

SUMMARY OF THE INVENTION

The invention has as its object to provide a process of the initiallydefined kind as well as a burner for carrying out the process, which areable to meet the following opposing demands in the optimum way: on theone hand, very good thorough mixing of the oxygen with the fuel is to beeffected, yet, on the other hand, whirling effects should not occur orbe kept as slight as possible. This is only difficult to realize, inparticular, if optimum thorough mixing is to be achieved also in themarginal region of the burner jet. Another object of the invention is tobe seen in rendering feasible output regulation within a wide range at aconstantly uniform flame development by one and the same burner; thus,the burner is to be operable within a wide range of capacity at a stableand uniformly long flame. In doing so, only slight changes in the flamethickness are to occur in the total range of capacity.

With a process of the initially defined kind, this object is achieved inthat a main jet of oxygen or an oxygen-containing gas is surrounded byseveral fuel jets oriented in a skew manner relative to-the centrallongitudinal axis of said main jet and the fuel jets are blown into themain jet which is approximately cylindrical or slightly conicallywidening in the jet direction, wherein the fuel jets are formed tosurround the main jet peripherally and have a greater distance from themain jet at the site of origin than shortly thereafter, if viewed in thedirection of flow, such that they penetrate into the main jet and aresucked into the main jet, wherein advantageously a further fuel jet offree hydrocarbons and/or fine-grained to dusty solid fuels is formedcentrally within the main jet, said further fuel jet being annularlysurrounded by the main jet.

A particularly stable flame within a very wide range of capacity may beachieved in that the main jet is accelerated to supersonic speed priorto the penetration of said fuel jets.

A burner for carrying out the process according to the invention, inparticular for use in a metallurgical vessel intended for the productionof liquid pig iron, steel preproducts or steel, is characterized by thecombination of the following characteristic features:

a first tube for forming a supply channel for oxygen and/or anoxygen-containing gas and a main jet of these gases,

a second tube surrounding the first tube while forming an annular gapfor supplying a fuel,

wherein the annular gap discharges toward the exterior by a plurality ofdischarge channels peripherally surrounding the first tube andpreferably designed as Laval nozzles, while forming individual fueljets, and

planes laid through the axes at mouths of the discharge channels anddisposed parallel to the longitudinal axis of the main jet intersect thepartial circle of the mouths, in a manner

that the fuel jets penetrate into the main jet.

Preferably, the first tube internally is designed as a nozzle,preferably as a Laval nozzle.

The invention also relates to the exchange of fuel for oxygen in amanner that the main jet is formed of fuel and the skew jets and theflow from the central tube, if present, are formed of oxygen or anoxygen-containing gas, as well as a burner designed accordingly.

When arranging the burner at a metallurgical vessel, the former suitablyis pivotably fastened to a supporting console arranged at themetallurgical vessel and projects inwardly through an opening of themetallurgical vessel for the purpose of supplying the fuel and/or theoxygen or oxygen-containing gas.

Advantageously, the burner is provided with a cover plate for coveringsaid opening, which has a larger diameter than the burner, whereinsuitably a plurality of damping plates sliding at one another andallowing for a pivotal movement of the burner are provided.

Furthermore, the burner advantageously is upwardly covered by aprotection plate.

Other advantages and features of the invention will be readily apparentfrom the following description of the preferred embodiments, thedrawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view with portions in elevation taken alonga central longitudinal axis of a burner of the present invention;

FIG. 2 is an enlarged cross-sectional view of the mouth of the burner ofFIG. 1;

FIG. 3 is an end view of the mouth taken from the direction of arrow IIIin FIG. 2;

FIG. 4 is a cross-sectional view of a mouth of an embodiment of theburner of the present invention; and

FIG. 5 is a partial cross-sectional view illustrating the installationof the burner of the present invention in a metallurgical vessel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The burner represented in FIG. 1 comprises a first tube 1, through whichoxygen and/or an oxygen-containing gas is supplied. That first tube 1extends in the direction of the central longitudinal axis 2 of theburner and is surrounded by a second tube 3, by which an annular gap 4is formed between the first and second tubes. Through that annular gap,solid, liquid or gaseous fuel 5 comprised of free hydrocarbons and/orfine-grained to dusty solid fuels capable of being conveyedpneumatically are supplied.

The inner side of the first tube 1, on the mouth end 6, which is formedby a separate mouth part 7 readily detachable from the first tube 1 bymeans of a screw connection, is configured in the manner of a Lavalnozzle, which has a converging entrance portion which opens into adiverging exit portion, so such that the oxygen and/or oxygen-containinggas emerges from the mouth part 7 at supersonic speed.

The front end 6 of the mouth part 7 is provided with a flange 8extending radially outwards, the flange 8 contacting the inner wall ofthe second tube 3 by its external periphery. Within the flange 8discharge channels 9 for the fuel 5 are provided, which are configuredin the following manner:

The central axes 10 of the discharge channels 9, which are arrangedabout the circumference of the first tube 1 in a uniformly distributedmanner, are oriented in a skew manner relative to the centrallongitudinal axis 2 of the burner (which is identical with the centrallongitudinal axis of the first tube 1). The normal projection of eachcentral axis 10 on a plane laid through the central longitudinal axis 2and through the mouth 11 encloses an angle α of between 2° and 8° withthe central longitudinal axis 2.

The central axes 10 of the discharge channels 9 enclose an angle β ofbetween 85° and 60° with a plane 12 oriented perpendicular to thecentral longitudinal axis 2 of the burner. Thus, each of the axes 10 hasa component along the axis 2, a component extending radially inwardtoward the axis 2 and a tangential component as shown in FIG. 3. Thiscauses the fuel jets 13 emerging from the discharge channels 9 topenetrate into the radially symmetrical main jet 14 formed of oxygenand/or an oxygen-containing gas and to be sucked in by the same whiledeveloping a radially inward spiral or helical mixing motion with slightwhirl formations and yet causing efficient mixing of the fuel 5 with theoxygen.

This also happens if the main jet 14 is formed of fuel and the jets 13oriented in a skew manner relative to the same are formed of oxygen oran oxygen-containing gas. It merely has to be taken care that the mixingratio of the two substances relative to each other remains the same inorder to reach the optimum combustion process.

As mentioned above, the mouth part 7 of the first tube 1 is readilyexchangeable such that mouth parts 7 including discharge channels 9adapted to the respective fuels may each be inserted in the burner.Thus, for instance, for liquid fuels it is suitable to configure thedischarge channels 9 as nozzles having small cross sections, namely asliquid spray diffusers. It is suitable to configure also the dischargechannels 9 as Laval nozzles.

The second tube 3 externally is surrounded by a third tube 15, wherein afurther annular gap 16 provided between the second tube 3 and the thirdtube 15 serves to feed air 17 or an inert gas. Thereby, it is feasibleto influence the shape of the flame in a simple manner. This third tube15 is provided with an internal cooling at least on the mouth side. Itprojects beyond the second tube 3, which, in turn, by its end projectsbeyond the end of the first tube 1, i.e., its end flange 8.

Centrally within the first tube 1 there is provided a central tube 18,which is kept in a precisely centrical position relative to the firsttube 1 by means of spacers 19. This central tube 18, which likewiseserves to supply fuel 5 in solid, liquid or dusty or fine-particle form,ends approximately on the level of the discharge channels 9; yet, itpreferably is displaceable relative to the first tube 1 by adisplacement means 20 schematically indicated in FIG. 1, thereby againbeing able to influence the flame formation.

The central tube 18 likewise comprises a readily dismountable mouth part21, which may, for instance, be exchanged for an oil quill. This mouthpart 21 is designed to taper in a frustoconical manner in the flowdirection of the oxygen, the tapering beginning approximately from thenarrow of the Laval nozzle-shaped inner side of the first tube 1. Theaperture angle γ of the conical part 21 of the central tube 18 amountsto between 0.1 and 4°. Preferably, the central tube 18 on its inner sidelikewise is designed in a tapering manner. The pressure of the fuel 5within the central tube 18 (closely before its mouth) is selected tocorrespond with that of the oxygen (closely before the mouth). Thepressure of the fuel 5 supplied via the discharge openings 9 may beselected to differ from the oxygen pressure, yet a fuel pressure thatcorresponds with the oxygen pressure is advantageous also in that case.

According to the embodiment represented in FIG. 4, the burner has nocentral tube 18. It has been shown that for this embodiment the firsttube 1 on its mouth in any event must be designed as a nozzle, a Lavalnozzle being preferred.

It is also feasible for the skew discharge channels 9 to be formed ofguide plates coiled helically around the longitudinal axis 2, which arearranged at the mouth-side end zone of the annular gap 4 and optionallyare recessed from the mouth-side end of the annular gap 4.

FIG. 5 illustrates the arrangement of a burner according to theinvention within a metallurgical vessel 22, the burner being pivotablymounted on the external side 23 of the wall 24 of the metallurgicalvessel 22 on a console 25 welded thereto. In order to supply the oxygenand the fuel 5, the burner by its rear end projects outwardly through anopening 26 of the wall 24 of the metallurgical vessel 22. For thepurpose of silencing noises, the burner is provided with a cover plate27 extending approximately perpendicular to its central longitudinalaxis, which cover plate, in turn, cooperates with damping plates 28arranged on the wall 24 of the metallurgical vessel 22 and allowing fora pivotal movement of the burner. To protect the burner from scrap andsteel and slag pieces falling down, a protection plate 29 is providedabove the burner, which likewise is fastened to the external side 23 ofthe wall 24 of the metallurgical vessel 22.

The burner according to the invention has the advantage of being usableuniversally, i.e., as a gas burner, as an oil burner or as a burner forpneumatically conveyable solid fuels. It is also feasible to process amixture of those fuels. Furthermore, the burner may be used forafterburning as well as for a combined burner/afterburning operation. Inaddition, the burner is easy to dismount, structurally simple and easyto survey and producible at low cost.

In the following, the use of the burner is indicated by way of severalvariants:

a) ratio oxygen--natural gas larger than 2:1 (molar ratio)

b) ratio oxygen--natural gas+oil larger than 2:1 (molar ratio)

c) ratio oxygen--oil larger than 2:1 (molar ratio)

d) exclusively oxygen; no natural gas and no oil

Points a) b) c) enable the burner to be employed as a burnersimultaneously functioning as an afterburning lance (surplus of oxygen).According to point d) the burner may be operated as a mere afterburninglance.

In the following, the use as a gas burner is going to be explained inmore detail:

CH₄ is supplied through the central tube 18. The first tube 1 serves tofeed pure oxygen, the mouth part 7 being designed as a Laval nozzle.Through the discharge channels 9 provided between the first tube 1 andthe second tube 3 CH₄ is supplied as well. The dimensions of the burnerare as follows: The internal diameter of the central tube 18 is 8 mm,the wall thickness of the central tube is 1 mm. The critical diameter ofthe mouth part 7 designed as a Laval nozzle, of the first tube 1 is 19mm. The internal diameters of the discharge channels 9 designed ascylindrical bores are 6 mm, six bores being uniformly distributed aboutthe circumference of the first tube 1. The following Table indicates thepressures and quantities of the oxygen fed and of the CH₄ :

    ______________________________________                                        Discharge channels                                                                              Laval nozzle   Central tube                                 P.sub.CH4 .sup.1)                                                                     Q.sub.CH4 P.sub.O2 .sup.1)                                                                     Q.sub.O2                                                                              P.sub.CH4 .sup.2)                                                                   Q.sub.CH4                              [bar]   [Nm.sup.3 /h]                                                                           [bar]  [Nm.sup.3 /h]                                                                         [bar] [Nm.sup.3 /h]                          ______________________________________                                        3        50       10     150     2.1   30                                     3       120       10     300     2.1   30                                     3       220       10     470     2.1   31                                     ______________________________________                                         .sup.1) Pressure within supply duct                                           .sup.2) Pressure within central tube in front of mouth                   

The use of the burner for the combined function of burner/afterburninglance or as a mere afterburning lance is feasible without any problem.The burner burns very stably within a relatively wide pressure range(depending on the critical diameter and on the prepressure of the media)and at a uniformly long constant flame. The flame thickness changes onlynegligibly within the total pressure range.

What is claimed is:
 1. A process for burning fuel which is composed offree hydrocarbons and/or fine-grained to dusty solid fuels, said processcomprising the steps of creating a main jet of oxygen-containing gas,accelerating the main jet to supersonic speed, and then surrounding saidmain jet with several fuel jets oriented in a skewed manner relative toa central longitudinal axis of the main jet, the fuel jets being blownhelically into the main jet which is approximately a cylindrical flow inthe jet direction, said fuel jets converging toward the main jet as theyflow skewed to the direction of the main jet so that they penetrate intothe main jet and are sucked into the jet.
 2. A process according toclaim 1, which includes introducing an additional jet of fuel centrallywithin the main jet so that the additional jet is annularly surroundedby the flow of the main jet.
 3. A process for burning fuel comprisingfree hydrocarbons and/or fine-grained to dusty solid fuels, said processcomprising the steps of creating a main jet of fuel having anapproximately cylindrical shape as it extends in a first direct,accelerating the main jet to supersonic speeds, and then surrounding themain jet with several jets of a combustion-supporting gas oriented in askewed manner relative to a central longitudinal axis of the main jet,said jets being blown helically into the main jet so that theoxygen-containing gases penetrate into the main jet, and providing anadditional jet of oxygen-containing gas and introducing it centrallywithin the main jet so that the additional jet is annularly surroundedby the main jet.
 4. A burner for carrying out a process of burning freehydrocarbon and fine-grained to dusty solid fuels, said burnercomprising a first tube connected to a supply for oxygen-containing gas,said first tube terminating in a nozzle discharging a main jet of saidgases, said nozzle having means for accelerating the main jet tosupersonic speeds a second tube surrounding the first tube and formingan annular gap with the first tube, said second tube being connected toa supply of fuel, said annular gap having a plurality of dischargechannels peripherally surrounding the first tube adjacent the nozzlethereof and forming individual fuel jets being skewed toward the firstjet so that the individual fuel jets penetrate helically into the mainjet.
 5. A burner according to claim 4, wherein the means foraccelerating comprises the nozzle of the first tube having a convergingentrance portion connected to a diverging exit portion.
 6. A burneraccording to claim 4, which includes a central tube connected to a fuelsupply duct being provided centrally within the first tube andterminating adjacent the nozzle of the first tube.
 7. A burner accordingto claim 6, wherein the central tube comprises a detachable mouth part.8. A burner according to claim 6, wherein the central tube terminates ina tapering surface at the mouth of the central tube forming a nozzleconfiguration within the nozzle of the first tube.
 9. A burner accordingto claim 8, wherein an aperture angle γ of the tapering surface of thecentral tube is between 0.1° and 4°.
 10. A burner according to claim 6,wherein the central tube has an end tapering toward the mouth adjacentthe nozzle of the first tube.
 11. A burner according to claim 6, whereinthe central tube is displaceably guided within the first tube in thedirection of the central longitudinal axis of the first tube.
 12. Aburner according to claim 4, wherein a nozzle end of the first tubecomprises a separate mouth part detachably connected with the first tubeby means of a screw connection.
 13. A burner according to claim 12,wherein the detachable mouth part of the first tube on a mouth side isprovided with a flange extending radially outward, said flangecomprising the discharge channels in the gap between the first andsecond tube.
 14. A burner according to claim 4, wherein the second tubeis surrounded by a third tube forming an additional annular gap forfeeding air and/or inert gases to the burner.
 15. A burner according toclaim 14, wherein the third tube has means for cooling the third tubewith water.
 16. A burner according to claim 4, wherein an axis of eachof the discharge channels of the second tube form an angle of between 2°and 8° with the central longitudinal axis of the first tube.
 17. Aburner according to claim 4, wherein the axis of the discharge channelsincludes an angle β of between 85° and 60° relative to a plane extendingperpendicular to the central longitudinal axis of the first tube.
 18. Aburner for carrying out a process for burning free hydrocarbons andfine-grained to dusty solid fuels, said burner comprising a combinationof a first tube for forming a supply channel for fuel and terminating ina nozzle discharging a main jet of the fuel, said nozzle having meansfor accelerating the main jet to supersonic speeds, a second tubesurrounding the first tube and forming an annular gap for supplyingoxygen and oxygen-containing gases, said annular gap discharging througha plurality of discharge channels peripherally surrounding the firsttube and constructed as nozzles to form individual jets, said nozzlesbeing skewed toward the main jet with axial, radial and tangentialcomponents so that the gases discharged by the nozzles penetratehelically into the main jet.
 19. A burner according to claim 18, whereina central tube connected to a source of oxygen-containing gas isprovided centrally within the first tube so that oxygen is dischargedcentrally within the main jet.
 20. A burner according to claim 19,wherein the central tube comprises a detachable fastening mouth part.21. A metallurgical vessel comprising a vessel having a wall with anopening, a supporting console arranged at the opening, a burner beingpivotably fastened to the support console and projecting into theopening, said burner having a first tube for forming a supply channelfor oxygen and/or oxygen-containing gas and terminating in a nozzlecreating a main jet of said gases, said nozzle having means foraccelerating the main jet to supersonic speeds, a second tubesurrounding the first tube and forming an annular gap for supplyingfuel, said annular gap having a plurality of discharge channelsperipherally surrounding the first tube and forming nozzles for creatingindividual fuel jets, said nozzles being skewed with radial, axial andtangential components toward the main jet so that the fuel jetspenetrate helically into said main jet.
 22. A metallurgical vesselaccording to claim 21, wherein the burner is provided with a cover platefor covering the opening, which is a larger diameter than the burner.23. A metallurgical vessel according to claim 21, which includes aplurality of dampening plates sliding on one another and allowing for apivotable movement of the burner.
 24. A metallurgical vessel accordingto claim 21, wherein the burner is upwardly covered by a protectiveplate.